1. Field of the Invention
The present invention relates to a motor vehicle having steerable front and rear wheels.
2. Description of the Relevant Art
When ordinary motor vehicles with steerable front wheels (hereinafter referred to as a "2WS motor vehicle") curve around a corner, they are required to make a quick turn and return to a straight course with good response upon turning of the steering wheel. There have been proposed in recent years various motor vehicles with steerable front and rear wheels (hereinafter referred to as a "4WS motor vehicle") for improved steering feeling. In such a 4WS motor vehicle, the angle through which the rear wheels are turned is always smaller than the angle through which the front wheels are turned. The 4WS motor vehicles are also required to make a turn and return to a straight course quickly in response to turning of the steering wheel.
In a 2WS motor vehicle, the rate of change of camber Cgf of the front wheels with respect to ground remains small for the full performance of the front wheel tires in a range from straight-course travel to a turn. In view of this advantage, many 2WS motor vehicles have double-wishbone independent suspensions associated with the front wheels. The rear wheels are combined with various suspensions such as link, swing-arm, semi-trailing, and full-trailing suspensions.
With a double-wishbone independent suspension, camber Cg of the wheel with respect to ground while the vehicle body is rolling during a turn remains substantially the same as camber Cg of the wheel with respect to ground during travel along a straight course. Stated otherwise, camber Cb of the wheel with respect to the vehicle body while the vehicle body is rolling varies from camber Cb of the wheel with respect to the vehicle body while in straight travel. This variation in camber depends on the direction and magnitude of rolling of the vehicle body which in turn depend on the direction in which the vehicle turns. Under a neutral condition in which the vehicle body is not rolling, the vehicle body lies parallel to the road surface, and hence camber Cg of the wheel with respect to ground is equal to camber Cb of the wheel with respect to the vehicle body. It is now assumed with reference to FIG. 7 of the accompanying drawings that while a motor vehicle 100 with two steerable front wheels Wf is running straight in a forward direction F, a lefthand rear wheel Wr rides on a road bump (not shown) with its upper surface inclined inwardly in the transverse direction of the vehicle. Now, the lower portion of this rear wheel Wr is displaced outwardly from its neutral position. As a result, an additional camber thrust Tc is produced inwardly in the transverse direction of the vehicle. The additional camber thrust Tc is transmitted through an arm of the rear wheel suspension (not shown) and other members to the vehicle body, which is then subjected to yawing counterclockwise (FIG. 7) about the center of gravity G of the vehicle. This problem also occurs when one of the rear wheels Wr is affected by some disturbance while the motor vehicle is turning.
The present invention has been made in an effort to meet the aforesaid requirement on 4WS motor vehicles and also to solve the problem which would be encountered with a 4WS motor vehicle having a double-wishbone independent suspension associated with a rear wheel.